FISHERY BULLETIN: VOL. 84, NO. 3 



thermometer observations) decreased with depth; 

 temperatures ranged from 5° to 13 °C at depths 

 <500 m and declined gradually from 5°C at 500 m 

 to 3.5°C at 1,900 m (Appendix Tables 1, 2). Depth- 

 temperature profiles of three Alvin dives (Fig. 6) 

 indicate depths of 500 to 600 m were a transition 

 zone; deeper bottom water temperatures decreased 

 little with depth, in comparison to shallower tem- 

 peratures. Cerianthids B, C, and D were seen at 

 temperatures of 5.3° to 13.0°C, and Cerianthid A 

 was observed only in colder, deeper water, in the 

 narrow range of3.5°to3.9°C (Appendix Tables 1, 

 2). 



0? 



Q 



X 



Q. 

 U 

 O 



10 



12 • 



TEMPERATURE (°C) 



2 4 S 8 10 



i i i i 1 1 r 1 i 



* - #576 

 - #578 

 + - #579 



Figure 6.— Depth-temperature profiles constructed from obser- 

 vations (of external thermometers) made on the bottom during 

 three Alvin dives in Veatch Canyon. Temperature stabilized at 

 about 500-600 m. 



Relation to Sediments 



Ceriantharia occurrence at grab sample stations 

 was not independent of sediment type (x 2 , P < 

 0.05); they rarely inhabited 100% gravel sediments 

 (Fig. 4). However, when stations with 100% gravel 

 sediments were not included, occurrence was in- 

 dependent of sediment type (x 2 , P > 0.05). Al- 

 though occurrence in silt-clay sediments was lower 

 than in other unconsolidated sediments (Fig. 4), this 

 may be a result of the large proportion of silt-clay 

 sediment stations at depths >500 m, where Ceri- 

 antharia were scarcer; if only silt-clay sediments 

 from shallower than 500 m are analyzed, occurrence 

 is more than 20%. 



Photographic transect profiles of submersible 



dives (Appendix Table 2, depths <400 m) provided 

 information on Ceriantharia abundance with respect 

 to substrate, depth, temperature, transect direction, 

 and distance (Figure 7 shows one profile). Based on 

 the number of sightings in various substrata (Ap- 

 pendix Tables 1, 2) and the transect profiles, about 

 70% of the Ceriantharia inhabited silt-sand and silt- 

 clay sediments. However, they also commonly 

 occurred in rarer gravelly substrates (less than 

 about 50% gravel cover on sand or clay; only about 

 20% of the total seafloor viewed). They were not 

 seen in coarse sand sediments (usually rippled and/or 

 in dune formations). 



The clay substrate observed from submersibles 

 was actually a semiconsolidated mud (Cooper et al. 

 in press); the term clay was used to differentiate it 

 from sand substrates, but clay may only be a minor 

 constituent. 



Spatial Pattern 



Ceriantharia density and biomass estimates from 

 grab sample data were determined for comparison 

 to other studies (e.g., Sanders 1956; Pearce et al. 

 1981; Reid et al. 1981; Caracciola and Steimle 1983). 

 However, because no replicate sampling was done 

 at over 90% of the stations, density and biomass 

 were not analyzed further. For stations with 

 anemones or whole tubes, mean density was 35.7 

 m" 2 (N = 168, 95% C.L. = ±12.1, range = 1.7 to 

 1,370 m~ 2 ). Mean station biomass (anemone blotted 

 wet weight) was 48.6 g m~ 2 (N = 139, 95% C.L. = 

 ±35.4). 



On the quantitative submersible dives, Cerian- 

 tharia density ranged from to 0.414 m~ 2 dive -1 

 (Appendix Table 2). The maximum density in one 

 photographic frame was 6.6 m~ 2 . The photographic 

 transect profiles (Fig. 7) showed Ceriantharia 

 populations shallower than 400 m were spatially ag- 

 gregated. No quantitative information was available 

 for the Cerianthid A populations seen in the axes 

 of Oceanographer and Veatch Canyons. 



The largest aggregation encountered (head of 

 Lydonia Canyon, Fig. 7) was over 0.5 km wide and 

 composed mostly of Cerianthid B, with some Cerian- 

 thid C individuals. The dives were run over a perma- 

 nent station marker (37 khz pinger) positioned on 

 a 14-15 m high knoll. Substrate atop the knoll was 

 gravel-sand, near the base and surrounding the knoll 

 was silt-sand. Approximately half of the Cerian- 

 tharia aggregation occupied the gravel-sand sedi- 

 ments. Ceriantharia were the dominant megafauna 

 in the area, other common megafauna were gala- 

 theid crabs, Munida iris Milne-Edwards, and 



634 



